Widely known in the art are uneven bars comprising two parallel handrails, two pairs of uneven uprights carrying the handrails on the top ends, bases supporting the uprights, two pairs of tensioning cables with turnbuckles and a handrail spacing adjuster.
The handrail spacing adjuster is essentially a lead screw with a crank at the end. The lead screw can be rotated and is pivotally connected to one of the uprights. The lead screw nut is rigidly fixed within a tube attached to the other related upright.
When rotated by the crank the lead screw displaces the nut, thereby altering the distance between the handrails.
These uneven bars are not provided with a cable tension control device and, therefore the tension of the cables changes so much after every adjustment of the bars that use of the turnbuckles and swivel tighteners is necessary to restore the cable tension to within 2750.+-.150 N (275.+-.15 kgf) as specified by the FIG. regulations. Much time is lost by such adjustment, and execution of exercises by gymnasts is accordingly hindered during competition.
Known in the art are also uneven bars of the NOUANSPORT Society, which comprise two parallel handrails, two pairs of uneven uprights, two pairs of tensioning cables provided with turnbuckles, handrail spacing adjusters arranged between the longer and shorter uprights and a cable tension control device.
The cable tension control device is actually a screw on which a slider (a nut) can move varying the tension of the bracing cable leg attached to the nut.
The handrail spacing adjuster and cable tension control device are interconnected mechanically, being actuated by a hand drive crank.
The handrail spacing adjuster is essentially a mechanism consisting of a lead screw and a nut fixed in a tube pivotally attached to the shorter upright. The nut moves along the lead screw connected with a gear-box whose case is rigidly mounted on each longer upright. Fixed on the lead screw running on the gear-box bearings is a gear meshed with another gear mounted on the hand drive crank axle. The gear mounted on the hand drive crank axle is in mesh with the cable tension control device gear.
The cable tension control device also comprises a lead screw carrying a gear rigidly attached to the screw and meshed with the gear mounted on the hand drive crank axle. Movable along the lead screw is a nut to which one end of the tensioning cable is attached and which is held against rotation by a pin snugly fit in the nut and slidably installed in the slots of the tube encasing the lead screw and the nut. The tube is securely fixed to the gear-box case. Such an arrangement provides alteration of the distance between the handrails due to rotation of the crank, with the cable tension being maintained constant.
However, an additional torque must be applied to the crank during adjustment of the handrail spacing with the cable tension kept constant. Considerable efforts and much time are needed to set the required distance between the handrails, which presents difficulty during competitions. For example, a team of six gymnasts can hardly accomplish warm-up exercises within the alloted warm-up time.